Electronics are increasingly desired for testing, control, measurement, actuation, and communication in downhole (i.e., in a wellbore) applications, such as measurement while drilling/logging while drilling (MWD/LWD) and directional drilling (or geosteering), wireline logging, coil tubing, slickline services, and the like. Downhole environments are harsh. Accordingly, electronics in a downhole environment may require being properly protected against high pressures, conductive fluids, corrosive chemicals, severe vibrations, and mechanical shocks that are in excess of their designed specifications.
A downhole tool is a self-enclosed unit which can perform specific functions, such as formation measurements, coring, fluid sampling, toolstring monitoring and so forth in a downhole environment. Downhole electronics comprise thousands of parts and components which are typically installed on various print circuit boards (PCBs). A tool typically comprises multiple electronics assemblies, such as printed circuit board assemblies (PCBAs) in order to achieve complex functionality. Given the harsh downhole operating environments, the electronic assemblies are typically installed in protective cavities to ensure reliable operation. For example, a tool may be constructed from high-strength metal or metal alloys and have a tubular or cylindrical body for easy deployment. The protective cavities within which the electronic assemblies are installed are dispersedly cut out from the metal to avoid creation of weak points in the tool body. Further, wireways, i.e., special long thin cavities are also created so that cables and harnesses can be used to interconnect the electronic assemblies for the data and power communication.
In some implementations, a bottom-hole assembly (BHA) includes a plurality of these protective packages (i.e., segments) connected end-to-end at segment joints. The BHA may include one or more tools in each of the segments. The tools are usually connected to a tool bus through which power and data can be communicated so that the tools operate collaboratively to complete complex downhole jobs. In most cases, the tool bus is further coupled to the surface via a telemetry tool for real-time communication, control, and power transmission. In practice, a segment is typically a drill collar, a drill sub, a pressure mandrel, and so forth.
Internally, the PCBAs of a tool are interconnected together via one or multiple harnesses. For easy service later on, harnesses are usually detachable. In practice, a PCBA is typically equipped with connectors at its one or both ends, and correspondingly a harness of stranded wires with mating connectors are interconnected by the stranded wires. When a tool is assembled, the mating connectors of a harness are securely joined to the corresponding connectors on the PCBAs with jackscrews. Therefore, different PCBAs of a tool can transmit data and power, or achieve specific purpose such as synchronization or control, etc, using the electrical connections provided by the wire harnesses.
Typically, micro D connectors conforming to the MIL-DTL-83513 standard such as ITT Cannon MDM series, AirBorn M series and the like are most widely used in downhole applications. A standard micro D connector has a selectable number of contacts from 9 up to 100 or more and also has different varieties in terms of configurations, temperature rating, materials and finishes. Although standard micro D connectors are readily available, mating harnesses are usually customized because the wire length, number of interconnections and mating connectors of the harnesses are dependent on the specific tool design. For example, different numbers of connections may be needed between different PCBAs of a tool. Typically, the mating harnesses have several tens to a hundred or more connections between the PCBAs of a tool. Despite the small profile of each stranded wire, based on the large numbers of connections, a wire harness may be large, taking up valuable space within a segment.
Historically, electronics development of a downhole tool is costly, lengthy and challenging. Given that downhole environments are usually much harsher than most electronics are designed for, tremendous efforts must be made to screen out the “tough” electronics with extra quality beyond what electronics suppliers can ensure. Typically, a multi-stage progressive development method is taken by the industry, of which each stage has a different test emphasis to simplify the instrumentation needs. Generally, downhole electronics are progressively tested at the component level, module level, assembly (e.g., PCBA) level, tool level, and toolstring level and culminate in a field trial. As the result, tool development is lengthy and expensive. Statistically, it takes about 3-5 years to develop a MWD/LWD tool, and 1-3 years for a wireline tool. A total capital expense of tens of million dollars is very common for a MWD/LWD tool, although it is a bit less for a wireline tool at the order of serval million dollars.
Today, oil/gas markets are more volatile than ever and the traditional development process hardly meets rapidly-changing industry needs.